In general, a liquid crystal display (LCD) is a device that individually supplies a data signal based on image information to pixels arranged in a matrix array and adjusts optical transmittance of the pixels to form a desired image. Since LCD cannot emit light by itself, a light unit is mounted to a rear of the LCD to produce an image.
Referring to FIG. 1, such a light unit 1 is configured so that a flat light guide plate 30 is placed on a substrate 20 and a plurality of side view LEDs 10 (only one of them is shown) is placed at a side of a light guide plate 30 in an array form.
Light L transmitted from the LED 10 to the light guide plate 30 is reflected upwards by a fine reflection pattern or a reflection sheet 40 formed on a lower surface of the light guide plate 30, exits from the light guide plate 30, and thereafter supplies back light to a LCD panel 50 located above the light guide plate 30.
As shown in the conceptual view of FIG. 2, the light unit may further include a plurality of optical sheets, including a diffusion sheet 31, prism sheets 32 and 33, and a protection sheet 34, between the light guide plate 30 and the LCD panel 50.
Such a light unit functions to uniformly illuminate the LCD, which cannot emit light by itself, from the back thereof to allow a display image to be seen. The light guide plate functions to provide uniform luminance and illumination to the light unit and is a kind of plastic molded lens uniformly delivering light from a light source (LED) to an entire surface of the LCD. Thus, such a light guide plate is basically used as an essential part of the back-light unit. However, the conventional light unit is problematic in that it is difficult to achieve thinness of an entire product because of the thickness of the light guide plate, and an image quality may be deteriorated in the case of a large-area back-light unit.
Further, the light diffusion plate or the diffusion sheet 31 of the conventional light unit for diffusing light has a shielding pattern to prevent light from being concentrated. Such a shielding pattern implements a light shielding effect using Ag. However, the optical pattern using Ag for obtaining the light shielding effect has a drawback in that a portion having the pattern is completely optically shielded, so that it is difficult to attain uniformity of light through an entire portion, and reliability of the light unit emitting white light is lowered because of yellow light emitted from the light source, the LED.